1. Field of the Invention
The present invention relates generally to a rotary machine, and more specifically to a method and an apparatus for sealing a rotary machine.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
In an industrial gas turbine engine, rotary seals are required to provide a seal between a rotating part (the rotor) and a stationary part (the stator) of the engine and prevent a hot gas flow from passing through to temperature sensitive areas and to prevent leakage of the hot gas in order to increase the efficiency of the engine. Labyrinth seals or brush seals have been widely used in these engines but have limitations. Brush seals will wear relatively easily due to a constant rubbing of the brush ends on the rotating surface that forms the seal surface. Brush seals make good low rotation speed seals. The labyrinth or lab seals provide good sealing at higher rotational speeds without rubbing, but provide high leakages at lower rotational speeds because of a gap formed between the ends of the lab seal teeth or fingers and the stationary part of the casing or housing that forms the seal interface for the brush lab seal. In some cases, the lab seals are designed to rub against a honeycomb structure to provide an even lower leakage flow across the lab seal.
Prior art card seals include an annular arrangement of leaf plates that are stacked on top of one another, where one end of each leaf plate is secured to the seal casing while the opposite end rides on and over a rotating surface such as a rotor shaft in which the seal is to be formed. The card seals are made such that the leaf plates can have a slight pivot about the top end that is secured to the seal casing, the slight pivoting allowing for play during operation of the card seal. The prior art leaf plates are flat surfaces and form a small controlled air gap between adjacent leaf plates. Card seals are like a combination of labyrinth seals and brush seals combined into one seal. Because an upstream side of the card seal is at a higher pressure than the downstream side, the pressure differential can force leakage through the leaf plates because of any gap formed between adjacent leaf plates. When all of the gaps for all of the annular arrangement of leaf plates are counted, a large leakage flow is formed across the card seal.
U.S. Pat. No. 6,736,597 B2 issued to Uehara et al. on May 18, 2004 and entitled AXIS SEAL MECHANISM AND TURBINE and U.S. Pat. No. 6,874,788 B2 issued to Kono on Apr. 5, 2005 and entitled STRIP BUSH SEAL discloses prior art card seals in which the leaf elements are just plane flat pieces stacked one on top of another to form a full 360 degree annular arrangement of leafs around a shaft. Because the leaf elements are flat, any small space formed between adjacent leaf elements will provide for a direct fluid leakage path from one side of the leaf elements to the opposite side.